DESCRIPTION (provided by investigator): This study application is a secondary analysis of an existing database in response to the Program Announcement, PA-09-265: Secondary Analyses of Existing Data Sets and Stored BioSpecimens to Address Clinical Aging Research Questions (R01) to determine influenza vaccine effectiveness in older adults. Recent work has shown that more is needed to be known about influenza vaccine effectiveness in older adults and the methodology used to determine that vaccine effectiveness. This database is an accumulation of three studies that prospectively tested older adults for influenza. This data will be used to determine if the current methodology of test-negative controls will actually control for the bias of frailty, will determine vaccine effectiveness in the very old, and will explore if vaccne manufacturing process impacts effectiveness.